The present invention relates to a method for driving an electromagnetic actuator for operating a gas change valve in which the actuator has at least one electromagnet and acts via an armature on the gas change valve against the force of at least one valve spring and operates the gas change valve by movement of the armature.
Electromagnetic actuators are usually used in internal combustion engines for operating gas change valves with which the inflow and outflow of a working fluid is controlled respectively into and out of the combustion chambers of the internal combustion engine.
Such an actuator is known, for example, from DE 196 31 909 A1. This previously known actuator has two electromagnets--a closing magnet and an opening magnet--with pole surfaces situated opposite to one another and an armature that can move axially between the pole surfaces of the electromagnets and which acts on the gas change valve to be operated in opposition to the force provided by two valve springs. In non-energized electromagnets, the armature is held securely in a position of equilibrium approximately mid-way between the pole surfaces of the electromagnets due to the oppositely acting valve springs.
By alternately energizing, i.e. switching on and off, the two electromagnets, the armature and hence also the gas change valve is attracted away from the position of equilibrium by the electromagnet being energized and held securely at the pole surface of this electromagnet for the period over which current is being applied. The gas change valve is than in a closed position when the armature is located against the pole surface of the electromagnet functioning as closing magnet, and in an open position when the armature is located against the pole surface of the electromagnet functioning as opening magnet.
In the previously known actuator, the position of equilibrium of the armature is determined by measuring the inductances of the two electromagnets and by a comparison of the two measured Inductance values, and in the event of a deviation from the desired value the position of equilibrium is readjusted.
Furthermore, from U.S. Pat. No. 4,823,825 it is known that in an actuator of the type named at the outset the impact of the armature on the energized electromagnet is detected by a brief drop followed by a renewed rise in an excitation current flowing through this electromagnet. The absence of this brief drop in the excitation current indicates that a faulty function has already occurred although this cannot be avoided, it is detected immediately and therefore allows measures to be initiated To rectify the fault.
The problem is unsolved, however, of eliminating in the control the influence of operational system parameters, especially fluctuations in friction, temperature and pressure in the combustion chambers as well as changes in the viscosity of the lubricant and wear or dirtying of the actuator or gas change valve. This can result in incorrect functioning of the actuator and in particular to increased wear of the actuator, undesired noise development end increased power consumption. Reliable continuous duty of the actuator is therefore not assured.